1. Field of the Invention
The present invention relates to the application of dry lubricants to metal substrates and, more particularly, to an enhanced friction-reducing surface and method by which a dry lubricant layer is applied both onto and into the metal substrate surface for enhanced wear performance over time.
2. Description of the Related Art
Films of friction-reducing dry lubricants such as molybdenum disulfide (MoS2), tungsten disulfide (WS2), graphite, etc. have been applied to various metal substrates, generally by spraying or dipping methods followed by drying or baking. Other methods such as chemical and vapor deposition have also been used.
The transfer of the dry lubricant film to the metal substrate according to these traditional methods is primarily a mechanical process by which a mixture of dry lubricant chemicals and peening particles is impacted against the substrate at a high enough velocity to adhere a thin layer of the dry lubricant chemicals to the top of the substrate surface. This thin layer may be adequate for certain limited applications, but when the treated surface is subjected to high wear, the dry lubricant is quickly removed. As a result, metal parts such as pistons, rings, bearings, journals, valve stems, shafts, and the like, which could greatly benefit from the low friction characteristics and protection provided by dry lubricants, are often excluded from treatment or obtain limited benefit therefrom due to the rapid deterioration in the lubricant coating in such high-wear environments.
In an effort to help the dry lubricants adhere to the surface of the substrate, some previous methods employ the use of solvents and binders. This is often unfavorable due to the added complexity and cost of the complex formulations of solvents, pigments, dispersants, binders and curing agents. Also unfavorable are the environmental health and safety concerns to be dealt with when using such compounds, as well as the dimensional build-up on the treated part.
Surface texturing has been found to be useful in helping to control friction and wear between two rubbing surfaces. Some of the known methods of surface texturing in use are machine methods such as turning, drilling, etc., laser texturing by drilling small holes using a laser, and electron beam texturing. These known methods require expensive equipment and the performance of a separate stage of treatment which is a disadvantage in that additional processing steps are required. These disadvantages are increased by the fact that no single texture type or size is sufficient for all applications such that the desired surface texture, including size and shape of features, must be determined on a case-by-case basis. This means that the expense and extra time associated with using the equipment may have to be repeated multiple times before the desired degree of surface texturing is determined and obtained.
Hence, there is a need for a method of surface texturing that can be performed simultaneously with the application of dry lubricant while offering control capability so as to be able to obtain variable levels of texturing in order to enhance surface performance specific to the end use of the treated substrate.
Also, so far as is known, no feasible way has emerged for treating metal surfaces with friction-reducing dry lubricant chemicals in such a way that the dry lubricant forms a long-wearing, high-endurance surface layer and in which the process required for application of the layer is manufacturer friendly.